Glaucoma

What is glaucoma?

Glaucoma is a group of eye diseases where the optic nerve suffers a progressive and irreversible damage. The common cause is a high pressure inside the eye - called ‘intraocular pressure’ or ‘IOP’. The high IOP compresses the blood vessels at the optic nerve. If left untreated, this progressive compression of blood supply leads to irreversible damage to the optic nerve. The field of vision, that is our ability to see the objects in the sides of our vision-line is affected. Ultimately the loss spreads to larger areas and may lead to total blindness. The central vision remains remarkably intact till the final stages, and so the patient will not be aware of the ongoing progressive damage.

What are the types of glaucoma?

The common type is open-angle glaucoma. The other is the angle-closure glaucoma, which may be acute (occurring suddenly) or chronic (slowly progressing).

What causes glaucoma?

While the entire body is nourished by blood, an ‘aqueous humor’ nourishes the lens, iris and cornea. This wonderful gift of nature keeps the optical pathway of our eyes clear. This aqueous humor is secreted by the ciliary body. After nourishing the various structures at the front of the eye it is drained out though a series of drainage canals in the trabecular meshwork. This delicate filter is located around the outer edge of the iris. When this meshwork gets blocked and as the liquid continuous to flow into the eye, the IOP builds up, causing glaucoma.

What are the symptoms?

Most people who develop glaucoma notice no symptoms until vision is impaired. Usually the peripheral vision is affected first. In the late stages when the optic nerve is completely destroyed, blindness results.
In rare cases of acute angle-closure glaucoma symptoms develop suddenly and rapidly progress to blindness if not treated. The doctor must be immediately contacted if there is:

• Blurring of vision
• Severe pain and redness of the eye
• Nausea and vomiting
• Haloes around lights

How it is diagnosed?

Glaucoma is essentially a clinical diagnosis, assisted by various tests. Some of them are:

• Raised intraocular pressure as measured with a tonometre
• Increased cup-disc ratio as diagnosed by stereo-ophthalmoscopy
• Analysis of visual fields by computerised perimetry
• Optic nerve head scanning with Heidelberg retinal tomography
• Corneal thickness with ultrasound pachymetry.
  
  

Those with a family history of glaucoma or diabetes, who have frequent headaches, experienced frequent change of glasses etc., should seek a detailed glaucoma screening. Glaucoma screening also needs to be a part of routine eye check up for everyone at or above the age of 40 years.

How is it treated?

Treatment is by reducing the raised intraocular pressure by medications, laser or surgery. As the disease lasts lifetime, the medicines need to be used for lifetime, or till the surgery is performed. Periodic follow-ups are essential, even after a surgery, to see that the disease progression has stopped.

Medications are generally in the form of eye drops. Follow doctor’s advice meticulously. Don’t reduce the doses on your own or change the drops or its brand. Don’t skip the drops and don’t change the advised timings. Understand the disease and its treatment well. If you are on multiple eye drops, give a gap of atleast 30 minutes and if possible an hour between different medications. To instill the drops, pull the lower lid out and put only one drop into the eye, with the face lifted up, towards the ceiling. It can fall on any part of the eye, and this does not matter. Close the eyes immediately, and let them remain closed for about 2 to 3 minutes. Even if the drop spills over from the eye, there is no need to put a second drop. Indeed a very tiny portion of an eye drop is enough for it to act. Keep the dropper bottle in a cool clean place.

Lasers are of use in Narrow angle glaucoma. A hole is lasered in the iris so that the aqueous bypasses the pupil. Lasers role in open angle glaucoma is extremely limited.

Surgery is preferred if the medications don’t control pressure adequately. You doctor may choose either penetrating trabeculectomy or the non-penetrating deep sclerectomy. These surgeries divert the aqueous into conjunctival tissues, bypassing the blocked trabecular meshwork. Often a wound modulating drug like Mitomycin or 5 FU are used to minimises scarring at the site of surgery, which closes the new channels in 40 to 45 % cases. The basic principle of the various surgical procedures is to provide a channel for the drainage of the fluid in the eye. Surgery for glaucoma may be done using a laser or by conventional operation. The operation is usually done after anaesthetising the eyeball. There is minimal discomfort. The operation usually lasts and hour. An eye patch is given which must be worn till the doctor advises. Medications to be instilled into the eye must be regularly used as advised by the doctor.

Early diagnosis and proper follow-ups are extremely important in glaucoma. Treatment can only control glaucoma, but cannot restore the sight that is already lost.

What are the complications of surgery?

As with any surgery, there are some risks with glaucoma surgery which include:

• Infection
• Bleeding
• Loss of vision

Before going in for the operation the patient must discuss all the options of treatment and the possible risks and benefits of surgery.